Explanation will be made on a conventional ultrasonic flow rate measurement device.
FIG. 14 is a view showing the cross-sectional configuration of conventional ultrasonic flow rate measurement device 100.
As shown in FIG. 14, ultrasonic flow rate measurement device 100 is provided with flow rate measuring tube 121 that allows a fluid to be measured to flow from one side to the other side. Moreover, ultrasonic sensor 122a is disposed on an upstream side whereas another ultrasonic sensor 122b is disposed on a downstream side, wherein ultrasonic sensors 122a and 122b are disposed opposite to each other while holding flow rate measuring tube 121 therebetween at a predetermined angle with respect to the center line.
Ultrasonic sensors 122a and 122b are contained in recesses 125a and 125b formed in the flow rate measuring tube 121, respectively. Bulk-like ultrasonic wave transmitting members 123a and 123b are housed inside of recesses 125a and 125b, respectively, thereby preventing the intrusion of the fluid to be measured into recesses 125a and 125b, followed by measuring a flow rate (see, for example, Patent Literature 1).
Additionally, FIG. 15 is a view showing the cross-sectional configuration of another conventional ultrasonic flow rate measurement device 150. As shown in FIG. 15, ultrasonic flow rate measurement device 150 has recesses 125a and 125b, in which ultrasonic sensors 122a and 122b are contained, respectively. Suppressing members 124a and 124b for restricting a fluid to be measured from flowing toward the sensors are disposed at openings, through which ultrasonic waves go onto a channel, at recesses 125a and 125b (see, for example, Patent Literature 2).
However, in the above-described conventional configurations, ultrasonic wave transmitting members 123a and 123b or suppressing members 124a and 124b are provided for suppressing the fluid to be measured from flowing into recesses 125a and 125b. Consequently, the disturbance of the flow of the fluid to be measured becomes small at a measurement part (i.e., an ultrasonic wave propagation path) at flow rate measuring tube 121 and recesses 125a and 125b, thereby reducing the degradation of measurement accuracy. However, the above-described configurations require separate members, and therefore, there arises a problem of an increase in cost due to an increase in material cost or number of man-hours.
In addition, a reception level of an ultrasonic wave in ultrasonic sensors 122a and 122b drops, and therefore, there arises a problem of difficulty of reduction of a drive input into ultrasonic sensors 122a and 122b. In view of this, when a gas meter for measuring domestic fuel gas such as town gas or LPG (liquefied petroleum gas) is kept to be used with a small battery capacity for as long a period as ten years, there arises a problem of difficulty in reducing power consumption.
PTL 1: Unexamined Japanese Patent Publication No. S63-26537
PTL 2: Unexamined Japanese Patent Publication No. 2004-101542